This invention relates to centrifugal pumps having impellers of radial, Francis vane, mixed flow, and axial flow design. In particular, this invention relates to an impeller for centrifugal pumps that is capable of producing a high head while pumping liquids of high viscosity and that is capable of pumping liquids having suspended solids without applying damaging forces to the solids.
A centrifugal pump conventionally has an impeller that rotates within a cavity in the body of the pump. Fluid flows to the impeller near its center of its rotation. Rotation of the impeller forces fluid to flow radially outward to an outlet from the cavity at a location that is radially adjacent to the impeller. Known centrifugal pump impellers have several recognized limitations and problems. One problem of such pumps is that operation to produce a high head output applies a significant force to the impeller that urges the impeller along its axis toward the pump inlet. The impeller must be supported sufficiently to carry the axial force without excessive displacement that will adversely affect the operation of the pump or diminish the satisfactory operational life of the pump.
Conventionally, the axial force applied to the impeller of a centrifugal pump is supported through the impeller drive shaft on which the impeller is mounted. The impeller drive shaft extends from the impeller through the pump body. Bearings that will support an axial load are used to support the impeller drive shaft and are mounted within the pump body. The pump body is sufficiently strengthened to support the impeller axial load that is transferred thought the impeller shaft and bearings. Alternatively, the axial force applied to the impeller may be supported by directly coupling the impeller drive shaft to the shaft of a motor that is constructed to support an axial force applied to the motor shaft. Whether the axial force is supported by a directly coupled motor or by a bearing in a strengthened pump housing, the structure that must be provided to support the axial load increases the cost of the pump.
Another problem of known centrifugal pumps is that operating the pump at high speed to produce a high head output causes a significant shearing force to be applied to fluid that flows through the pump. High viscosity fluids resist shearing forces and apply a significant load to the impeller when subjected to high shearing forces. This shearing force limits the use of such pumps to low pump speed and low output head for applications in which the fluid moving through the pump should not be subjected to such shearing forces. Fluid having high solids content, such as those that may be found in food processing systems, pharmaceutical processing systems, or clay slurries, are examples of applications in which a high shearing force may be unacceptable due to the potential for damaging the solids within the fluid. Such concerns either limit the pumping capacity of the centrifugal pumps in such systems or may preclude use of such pumps.
There is a need for an improved impeller centrifugal pump that overcomes the disadvantages and limitations of conventional impeller centrifugal pumps. In particular, there is a need for an improved impeller pump that does not require the expensive structure and mechanical components that support the axial load applied to the impeller of the conventional impeller centrifugal pumps. Further, there is a need for an improved impeller centrifugal pump that can operate at high speeds and produce a high head with less shear forces than current designs allow.
The present invention overcomes disadvantages and limitations of known impeller centrifugal pumps. The present invention provides an impeller for a centrifugal pump that is subject to lower axial forces during operation than prior impellers. This invention also provides an impeller for a centrifugal pump that subjects fluid moving through the pump to lower shear forces than do known centrifugal pump impellers.
More particularly, the impeller of the present invention has vanes having the radial edges formed into a hydrofoil that creates xe2x80x9cliftxe2x80x9d as fluid moves over the radial edge of the vane. The xe2x80x9cliftxe2x80x9d is applied to the impeller vane in a direction that opposes the axial force that is applied to the vane as a result of the impeller forcing fluid from the center to the radial edges of the impeller.
In another aspect, the vanes of an impeller according to the present invention limit the forces applied to fluid flowing past the impeller. The vanes are configured to have a circumferential width and axial length that directs fluid past the impeller along a smooth path thereby avoiding the shearing forces associated with abrupt changes in the flow path of a fluid. In addition, each vane has a cross section which creates an extended slip path from the high pressure side of the vane to the low pressure side of the vane. This extended slip path improves the efficiency of the impeller by reducing the amount of fluid that can move from the high pressure side of the vane to the low pressure side of the vane within the pump. Reducing fluid recirculation within the pump from the high pressure side of the vane to the low pressure side of the vane reduces the amount of shearing forces felt by the fluid.
Accordingly, it is an object of the present invention to provide an impeller for a centrifugal pump that will create a lower axial force during operation than prior impellers for radial impeller centrifugal pumps. This is accomplished by incorporating a hydrofoil that creates a lift force applied to the impeller in a direction that opposes the axial force created by the action of the impeller forcing fluid through the pump.
It is yet another object of the present invention to provide an impeller for a centrifugal pump that forces fluid through the pump along a path that is sufficiently smooth to avoid the high shear forces in the fluid that result from abrupt changes in direction of flow through the pump.
It is still another object of the invention to provide an impeller for a centrifugal pump that reduces recirculation of fluid within the pump.
These and other objects and advantages of the present invention will be understood from the following description and drawings of an embodiment of an impeller according to the present invention.